Resistance of the German cockroach (Blattella germanica) to bendiocarb

SUMMARY Two field strains of the German cockroach Blattella germanica (L.) were collected in England from survivors of treatments with bendiocarb wettable powder, and bred in the laboratory. These and a laboratory susceptible strain were compared by a tarsal contact method to test for resistance to bendiocarb, fenitrothion and dieldrin. The field strains after exposure to the insecticide for 24 h were resistant to bendiocarb in terms of mortality by factors of 5.6 and 6.2 at the LC50 level, but at the LC95 level the resistance factors were only 1.7 and 2.0; however knockdown resistance was detected, with resistance factors at the KD50 level of 10.6 and 8.1. At shorter exposure times of 5 min and 60 min, 2–20% of cockroaches from the field strains survived 55 or 110 mg bendiocarb/m2; there were no survivors from the susceptible strain. Some cockroaches from the field strains were able to recover from knockdown after and during exposure to 110 mg bendiocarb/m2. Both field strains showed some resistance to dieldrin; however, there was no resistance to fenitrothion. When all three strains were exposed to 55 mg fenitrothion/m2 for 5 min, all the insects were knocked down within 3 h, and all had died within 96 h. There was no recovery from knockdown to fenitrothion or dieldrin.